Organic materials such as high molecular weight materials or polymers are widely utilized as protective materials for various kinds of thin layers formed by vacuum vapor deposition. These organic materials are useful because of their excellent properties such as moisture resistance, durability, chemical resistance, insulating property, etc. In conventional techniques, these organic protective materials are formed on materials to be protected by coating, spraying, dipping, etc., e.g., as described in detail in Coating Technology (Kohtingu Kohgaku), published by Asakura Book Store, pages 253 to 277 (Mar. 20, 1971). Although these methods are suitable for the formation of a relatively thick protective layer, it is difficult to form a uniform thin layer having a thickness of less than, for example, 1 .mu.m conventional methods.
Recently, with the progress of thin metal layer-type magnetic recording media for the purpose of high-density recording, a very thin organic protective layer of about 50 to 1,000 .ANG. thick has been required. A so-called vacuum thin layer method typified by vacuum evaporation coating can form a very thin uniform layer. Such a method is thought of as being useful for forming a protective layer suitable for the foregoing purpose.
In a vacuum deposition method, as referred to above, a desired thin vapor-deposited layer is formed on a support by evaporating a material under heat in a vacuum atmosphere. This method has, hitherto, been utilized on inorganic evaporation sources such as metals, etc., as well as some organic evaporation sources.
However, when evaporating a high molecular weight material such as an organic polymer, etc., by heating in vacuum, the high molecular weight material is decomposed or gasified before it is sufficiently evaporated. Accordingly, the material does not attach to the article to be vapor-deposited. Furthermore, even if the high molecular weight material is vapor-deposited on an article, it forms decomposition products or has a reduced molecular weight. Thus, it frequently forms a layer having different properties from those of the evaporation source material before evaporation. Accordingly, it is difficult to form a film or layer of the same material as the organic polymer before evaporation. In view of the above, it can be seen that there are problems in the practical use of vacuum evaporation coating for organic polymers.
The material vapor-deposited on an article to be vapor-deposited is not always same as a polymer used as the evaporation source. However, it is sometimes desirable that the material formed by the vapor deposition be different from the material used as the evaporation source. That is, it is desirable to form a thin organic film or layer having desired properties with good reproducibility, at low cost, and at a high speed. Therefore, it has been desired to continuously form a thin organic film or layer by vapor deposition with good reproducibility and at good efficiency. However, no suitable methods for forming such a layer have been found. For example, Japanese Patent Publication No. 17440/64 and GB No. 991840 disclose a method of forming a polymer film by evaporating an organic polymer as an evaporation source by irradiation with a high energy electron beam while maintaining the polymer at a temperature below its decomposition point.
However, in the foregoing method, a charge up phenomenon of the evaporation source material occurs due to the irradiation with the electron beam. Accordingly, difficulties such as discharging, etc., are very likely to occur, making it very difficult to continue stable vapor deposition for a long period of time. Also, it is very difficult to continue stable electron beam irradiation while preventing the decomposition of the evaporation source material and the reduction in vacuum due to the decomposition.
Japanese Patent Publication No. 45989/74 discloses a method of fusing a non-thermoplastic resin by heating and continuously extruding the fused resin onto the surface of a heated drum disposed in a vacuum atmosphere by means of a pump in order to attach the resin to the surface of the drum. A thin vapor-deposited layer of the resin is formed on a material to be vapor-deposited by evaporating the resin on the surface of the drum under heat. However, in this system, it is necessary to completely evaporate the organic polymer attached to the drum. Therefore, the selection of the temperature of the drum and the selection of the supplying amount of the organic polymer are very complicated. In particular, in the case of an organic polymer having a relatively high decomposing property, the unevaporated polymer remains on the drum if the temperature of the drum is too low. However, if the temperature of the drum is too high, a carbonized residue formed by the decomposition of the polymer accumulates on the surface of the drum. Since these materials remaining on the surface of the drum obstruct the heat conduction from the drum, it is difficult to continually perform stable vapor deposition for a long period of time.
Japanese Patent Publication No. 21907/78 discloses a method of vapor-depositing polyethylene and polypropylene by maintaining these polymers at the optimum evaporation temperature. However, this method cannot be applied widely due to the limited number of materials which can be vapor-deposited by this method.
On the other hand, as a vapor deposition method of an alloy composed of elements each having different vapor pressure or of a decomposable compound, a so-called flash vapor deposition method has been used. In the flash vapor deposition method, an evaporation source material is completely evaporated by continuously supplying the material, little by little, to a heat-evaporating section, which is preheated and maintained at a high temperature.
It is not impossible to apply the flash vapor deposition method to organic polymers. Unlike inorganic materials such as alloys, etc., an organic polymer is partially decomposed and carbonized if abruptly heated. The carbonized product accumulates as residue. Therefore, when using the flash vapor deposition method, it is difficult to evaporate an organic polymer with good reproducibility over a long period of time.
As described above, it is impossible to continuously vapor-deposit an organic polymer with good reproducibility over a long period of time in conventional vapor deposition methods. Accordingly, the development of new vapor deposition method is desired.